Incorporation by reference is the act of including a second document within another document by only mentioning the second document. This act, if properly done, makes the entire second document a part of the main document. Incorporation by reference is often done in creating laws as well as in contract law and trust and estate law.

In law regarding wills, it is a doctrine at common law

Common law

Common law is law developed by judges through decisions of courts and similar tribunals rather than through legislative statutes or executive branch action...

 which allows a testator, or a creator of a will, to dispose of assets in his estate in accordance with a separate document. To be valid, such a document must comply with the following requirements:

1. it must have existed at the time the will was executed;
2. the will must describe the document with particularity, so that it may be identified; and
3. the will must clearly manifest the intent that the document be incorporated.

An exception to the first requirement is made for small gifts of tangible personal property

Personal property

Personal property, roughly speaking, is private property that is moveable, as opposed to real property or real estate. In the common law systems personal property may also be called chattels or personalty. In the civil law systems personal property is often called movable property or movables - any...

, such as household furniture and items of sentimental value.

Oral instructions can not be used as incorporation by reference. For example, if a testator states in the will that he has recited to a third party the intended disposition of testamentary assets, such attempt to circumvent the requirements of a written will is void.